China is now the biggest export market for countries as far afield as Brazil (accounting for 12.5% of Brazilian exports in 2009), South Africa (10.3%), Japan (18.9%) and Australia (21.8%). But exports are only one component of GDP. In most economies of any size, domestic spending matters more. Thus exports to China are only 3.4% of GDP in Australia, 2.2% in Japan, 2% in South Africa and 1.2% in Brazil (see map).

Even accounting for a 'ripple effect' from exports doesn't make China much more significant:

Export earnings can, of course, have a ripple effect throughout an economy. In Alpha, the prospect of selling coal to China is stimulating investment in mines, railways and probably even policing. But these “multipliers” are rarely higher than 1.5 or 2, which is to say, they rarely do more than double the contribution to GDP. Moreover, just as expanding exports add to growth, burgeoning imports subtract from it. Most countries outside East Asia suffered a deteriorating trade balance with China from 2001 to 2008. By the simple arithmetic of growth, trade with China made a (small) negative contribution, not a positive one.

And most compellingly, when Japan entered its first lost decade, it was a far larger share of the global economy than China, but the world economy barely flinched:

In April the Bank Credit Analyst, an independent research firm, asked what would happen if China suffered a “hard landing”. Its answer to this “apocalyptic” question was quite “benign”. As it pointed out, Japan at the start of the 1990s accounted for a bigger share of GDP than China does today. Its growth slowed from about 5% to 1% in the first half of the 1990s without any discernible effect on global trends. It is hard to exaggerate China’s weight in the world economy. But not impossible.

The implication is that a surprise China slow-down might not be the global risk we think it is.